1. Field of the Invention
This invention relates to a magnetic head suitable for recording and reproduction on and from a high coercive force magnetic recording medium, such as the so-called metal tape. More particularly, it relates to a magnetic head wherein the major portions of the magnetic core half or magnetic core halves are formed of an oxide magnetic material and the vicinity of the magnetic gap is formed of a soft magnetic alloy thin film or films.
2. Statement of the Related Art
In magnetic recording and reproducing apparatus, such as video tape recorders or VTRs, attempts have been made to increase the recording density of information signals. In keeping therewith, so-called metal tapes in which powders of magnetic metals such as Fe, Co and Ni are used as the magnetic powders, or so-called evaporated tapes in which the above metal material is directly deposited by evaporation, are increasingly used as the magnetic recording medium.
This type of the magnetic recording medium has higher coercive force and higher residual magnetic flux density so that a sufficiently high saturation magnetic flux density compatible with the coercive force of the recording medium is required of the core material of the magnetic head adapted for electro-magnetic conversion of information signals. Above all, when one and the same magnetic head takes charge of both recording and reproduction, not only the aforementioned saturation magnetic flux density but also a sufficiently high magnetic permeability for the relevant frequency range is required of the core material of the magnetic head.
However it is impossible with the conventional ferrite head to achieve sufficient recording characteristics for the aforementioned magnetic recording medium since the ferrite head has a high magnetic permeability but a low saturation magnetic flux density. On the other hand, the magnetic head constituted of a soft magnetic alloy material such as Fe-Al-Si system alloy has a higher saturation magnetic flux density and exhibits good recording characteristics for the high coercive force magnetic recording medium, but it has a low effective magnetic permeability for the working frequency range for the core thickness proper to the customary head shape so that its reproduction characteristics are deteriorated.
In view of the above, there has been evolved and utilized a magnetic head in which magnetic core halves are formed of a composite magnetic material of ferrite and Fe-Al-Si system alloy and the abutting surfaces of the thin films of the Fe-Al-Si alloy are used as the magnetic gap.
Above all, the magnetic head in which the aforementioned thin films of the Fe-Al-Si system alloy are provided only in the vicinity of the abutting surfaces of the ferrite portions and in which the boundary surfaces between the ferrite and the Fe-Al-Si alloy run substantially parallel to the magnetic gap surfaces, is advantageous in that the track width can be set without regard to the thickness of the Fe-Al-Si alloy and that the manufacture process is substantially the same as that for the conventional ferrite head so that it is superior in productivity and production yield.
However, with this type of the magnetic head, a layer affected by the reaction between the ferrite and the Fe-Al-Si system alloy tends to be formed on the ferrite surfaces, that is, on the surfaces where the Fe-Al-Si alloy thin film is formed, during the time such film is formed as by sputtering.
With the above magnetic head, the boundary surface between the ferrite and the thin film of the Fe-Al-Si alloy is substantially parallel to the magnetic gap surfaces in the vicinity of the magnetic gap, so that the aforementioned affected layer acts as the pseudo or false gap to affect in turn the reproduction characteristics of the magnetic head. Thus the pseudo gap causes the frequency characteristics of the reproduction output to be waved to deteriorate the quality of the reproduced image.
In addition, with a magnetic head in which the aforementioned core halves are constituted of a composite magnetic material of, for example, Mn-Zn ferrite having a thermal expansion coefficient of 115 to 130.times.10.sup.-7 /.degree.C. and the thin film of the Fe-Al-Si system alloy having a thermal expansion coefficient of 150 to 160.times.10.sup.-7 /.degree.C., the ferrite portions tend to be warped due to the differential thermal expansion coefficients between the different materials thus resulting in film peeling and promoting the ill effect of the pseudo gap while the mechanical strength of the magnetic head can not be elevated as desired.
For obviating the ill effect proper to the pseudo gap, there has also been proposed a magnetic head in which the boundary surface in the vicinity of the magnetic gap is inclined at a predetermined angle with respect to the magnetic gap to obviate the pseudo signals by taking advantage of the so-called azimuth loss. However, in production, this type of the magnetic head has a number of disadvantages, such that the machining of the head is complicated, the operation of forming the Fe-Al-Si film is time-consuming since the track width depends on the thickness of the thin film of the Fe-Al-Si alloy and that the productivity and hence the production yield are lowered.